Flaviviridae is a family of enveloped positive-strand RNA viruses which mainly infect mammals and birds.

[2][4] Members of the family Flaviviridae have monopartite, linear, single-stranded RNA genomes of positive polarity, and 9.6 to 12.3 kilobase in total length.

The 5'-termini of flaviviruses carry a methylated nucleotide cap, while other members of this family are uncapped and encode an internal ribosome entry site.

The genome encodes a single polyprotein with multiple transmembrane domains that is cleaved, by both host and viral proteases, into structural and non-structural proteins.

Among the non-structural protein products (NS), the locations and sequences of NS3 and NS5, which contain motifs essential for polyprotein processing and RNA replication respectively, are relatively well conserved across the family and may be useful for phylogenetic analysis.

[6][7] Many of the well-known members of the family causing disease in vertebrates are transmitted via arthropod vectors (ticks and mosquitoes).